Influence of Pre-existing Anti-capsid Neutralizing and Binding Antibodies on AAV Vector Transduction

Abstract

Pre-existing immunity to adeno-associated virus (AAV) is highly prevalent in humans and can profoundly impact transduction efficiency. Despite the relevance to AAV-mediated gene transfer, relatively little is known about the fate of AAV vectors in the presence of neutralizing antibodies (NAbs). Similarly, the effect of binding antibodies (BAbs), with no detectable neutralizing activity, on AAV transduction is ill defined. Here, we delivered AAV8 vectors to mice carrying NAbs and demonstrated that AAV particles are taken up by both liver parenchymal and non-parenchymal cells; viral particles are then rapidly cleared, without resulting in transgene expression. In vitro, imaging of hepatocytes exposed to AAV vectors pre-incubated with either NAbs or BAbs revealed that virus is taken up by cells in both cases. Whereas no successful transduction was observed when AAV was pre-incubated with NAbs, an increased capsid internalization and transgene expression was observed in the presence of BAbs. Accordingly, AAV8 vectors administered to mice passively immunized with anti-AAV8 BAbs showed a more efficient liver transduction and a unique vector biodistribution profile compared to mice immunized with NAbs. These results highlight a virtually opposite effect of neutralizing and binding antibodies on AAV vectors transduction.

Capsid-specific removal of circulating antibodies to adeno-associated virus vectors

“…Conversely, as expected, the Control animal had the lowest VGCN in most tissues except for spleen ( Fig. 1b), consistent with the expected biodistribution of AAV vectors in animals presenting anti-AAV antibodies at the time of vector administration 29,30 . The liver appeared to be the highest targeted organ, with VGCN in the Plasmapheresis animal ~1 log higher than the Control animal ( Fig.…”

“…In the setting of autoimmunity and transplant, purified human IgG (intravenous immunoglobulin, IVIg) is commonly supplied in combination with plasmapheresis to replenish the pool of circulating antibodies 28 . However, this would not be feasible in the setting of AAV gene transfer due to the fact that IVIg contains high-titer anti-AAV antibodies 29 .…”

Oracle or false prophet? Can we predict AAV efficacy based on preexisting antibody titers?

“…14 predictors of the outcome of gene transfer. 15 Others have suggested that in vivo neutralization assays, in which Nabs are passively transferred to mice following human serum injection to the animals, are more sensitive than those neutralization assays performed in vitro and thus better suited for inclusion/exclusion criteria. 16 However, neutralizing assays (both in vivo and in vitro) rely on the ability of a reporter vector to transduce the target cells and mediate quantifiable expression levels that decrease proportionally to the amount of circulating transduction inhibitors.…”

“…On the first question, the authors suggest that, while the transduction inhibition assay is considered a standard, a positive signal in either test (binding or neutralizing activity) should trigger exclusion from trials where AAVs are delivered systemically. This notion, perhaps prudent in principle, has been recently challenged by Mingozzi and colleagues on the grounds that binding antibodies may in fact increase capsid internalization and transgene expression and thus NAb assays are better predictors of the outcome of gene transfer . Others have suggested that in vivo neutralization assays, in which Nabs are passively transferred to mice following human serum injection to the animals, are more sensitive than those neutralization assays performed in vitro and thus better suited for inclusion/exclusion criteria .…”

Rescuing AAV gene transfer from antibody neutralization with an IgG-degrading enzyme

“…In humans, serological studies reveal a high prevalence of NAbs in the worldwide population, with about 67% of people having antibodies against AAV1, 72% against AAV2, and ∼ 40% against AAV serotypes 5 through 9(4, 12–14). Because of this high NAb sero-prevalence, screening for AAV antisera through in vitro NAb assays or ELISA is common place in AAV gene therapy trials and exclusion criteria can render upwards of 50% of patients ineligible for treatment or admission into clinical trials(15, 16). Furthermore, vector immunogenicity represents a major challenge in re-administration of AAV vectors.…”